You should use modifier SA for supervised nurse practitioner services when the insurer requires the modifier. Some Medicaid programs such as Medi-Cal require you to apply Modifier SA to all NP services which are submitted under the physician provider number.
Example: A nurse practitioner provides a level III established patient office visit to a Medi-Cal patient. The NP’s FP supervises the service. To indicate the NP provided the office visit under direct supervision, you would append modifier SA to 99213.
Use modifier SA for incident-to services that are billed under the supervising physician’s NPI number. The modifier tells the insurer that the NP rather than the physician provided the service and the physician supervised the NP. Incident-to services are paid at 100 percent of the Medicare Physician Fee Schedule amount.
Insurers may apply a reduction to services billed directly under the NP’s NPI. Typical reduction is 15 to 20 percent.